LCDs are widely used in various modern information products, such as notebooks, personal digital assistants (PDAs), video cameras and the like. The wide usage of the LCD is due to its advantages such as portability, low power consumption, and low radiation. LCDs are passive optical devices. That is, in general, a backlight module is needed to provide sufficient illumination for an LCD panel, so as to enable the LCD to display images.
Generally, the backlight module includes a surface light source. The surface light source usually includes either a plurality of line light sources such as cold cathode fluorescent lamps (CCFLs), or a plurality of point light sources such as light emitting diodes (LEDs). A CCFL is large and consumes much power. Therefore, the CCFL is more suitable for a large-sized multicolor display device requiring high-level brightness. The size of an LED is smaller, and light beams emitted by the LED are more focused. Therefore, the LED is more suitable for a small sized product, such as an LCD used in a mobile phone or a portable media player.
FIG. 7 is an exploded, isometric view of a conventional LCD. The LCD 100 includes a liquid crystal panel 11, and a backlight module 10 for illuminating the liquid crystal panel 11. The backlight module 10 includes a flexible printed circuit board (FPCB) 110, a light guiding plate (LGP) 120, a frame 130, and four LEDs 140.
The frame 130 includes a first sidewall 131 and a second sidewall 138 opposite to the first sidewall 131. The first sidewall 131 includes four recesses 132 generally facing toward the second sidewall 138. Each of the recesses 132 corresponds to one LED 140. The LGP 120 includes a light emitting surface 121, and a light incident surface 122 adjacent to the light emitting surface 121. The FPCB 110 includes a main part 112, and an extending part 111 extending perpendicularly from an end of the main part 112.
FIG. 8 is an enlarged view of one LED 140. The LED 140 includes a plastic shell 141, and an illuminant (not shown) disposed inside the plastic shell 141. The plastic shell 141 includes a light emitting portion 142, a first supporting portion 1411, and a second supporting portion 1412. The first and second supporting portions 1411 and 1412 are disposed at one side of the LED 140, and the light emitting portion 142 is disposed at an opposite side of the LED 140.
In assembly, the LEDs 140 are attached on the main part 112 of the FPCB 110, and the LGP 120 is received in the frame 130. Then the FPCB 110 together with the LEDs 140 is disposed on one side of the frame 130. Thereby, each of the LEDs 140 attached on the FPCB 11 is contained in the correspond recess 132 of the frame 130, with the light emitting portion 142 of the LED 140 facing the light incident surface 122 of the LGP 120. Finally, the liquid crystal panel 11 is disposed on the assembled backlight module 10, adjacent to the light emitting surface 121 of the LGP 120.
With this configuration, the LEDs 140 are located in the recesses 132 of the frame 130. Each recess 132 is usually slightly larger than the corresponding LED 140, in order that the LED 140 can be conveniently received in the recess 132. Thus, once the backlight module 10 assembled, a gap may exist between the light emitting portion 142 of the LED 140 and the light incident surface 122 of the LGP 120. For example, the width of the gap may be as much as 0.4 μm (microns). The light utilization efficiency of the LED 140 is reduced by the gap. Thus, the brightness of the backlight module 10 is reduced by such gaps. Furthermore, the greater the width of each gap, the greater the reduction in brightness of the backlight module 10. Moreover, due to random error inherent in the process of mass manufacturing the backlight module 10, the widths of the gaps may be different. These differences in width are liable to reduce the uniformity of the light output from the backlight module 10. As a result, display characteristics of the LCD 100, such as brightness and contrast ratio, may be degraded.
It is therefore desired to provide a backlight module that can overcome the above-described deficiencies, and an LCD employing such backlight module.